Microelectromechanical system (MEMS) devices employ the use of semiconductor fabrication techniques to create microscopic mechanical structures on the surface of a substrate. In the production of MEMS gyroscopes and accelerometers, for example, such fabrication techniques are utilized to create a number of moving structures on the substrate that can be used to sense displacement and/or acceleration in response to movement of the device about an input or “rate” axis. In navigational and communications systems, such moving structures can be used to measure and/or detect slight variations in linear and rotational motion of an object traveling through space. In other applications such as automotive systems, for example, such moving structures can be used in vehicle dynamic control (VDC) systems and antilock braking systems (ABS) to sense changes in vehicle and tire motion.
The packaging of MEMS devices remains a significant hurdle in the fabrication process. Typically, MEMS devices are fabricated by first removing a portion of the substrate surface to form the moving structures of the device, and then bonding the processed substrate to a cap that hermetically seals the structures within an interior cavity. In some designs, for example, the moving structures can be formed on the surface of the substrate using an etching and/or grinding process, and then subsequently attached to the cap using a suitable bonding process such as thermocompression bonding or thermoelectric (e.g. anodic) bonding. Once the substrate is processed and capped, a separate packaging structure is then fabricated and secured about the assembly to protect the contents. In some techniques, a lead frame can be coupled to the substrate to provide a means for electrically connecting the MEMS device to other external components, if desired.
Due to their size and composition, the mechanical structures of many MEMS devices are extremely susceptive to damage in high-G applications, and from particles, moisture or other such contaminants that can become entrained within the interior cavity of the capped substrate. In some cases, the difficulty in accurately regulating the pressure within the interior cavity during the fabrication process may affect the vibration characteristics of the device, reducing its efficacy in detecting subtle changes in motion. The process of separately forming the substrate and package and then connecting the two members together to form the final structure is often expensive and time-consuming, and may require additional steps be performed during fabrication. Moreover, such techniques do not resolve the issues of contaminants introduced within the interior cavity that can cause a reduction in device performance. As such, there is a need for robust packaging solutions for MEMS devices that offer both superior vacuum performance and protection against high-G environments while also providing high volume throughput and low cost.